1. Field
The present disclosure relates generally to orientation systems, and more specifically to a method and apparatus for sensing roll, pitch and yaw in a moving body, in addition to linear translation of the body in three-dimensional space.
2. Background
There exists a large variety of sensors available for detecting or measuring physical conditions or phenomena. A type of sensor commonly deployed in many industrial, commercial, or scientific contexts is a linear accelerometer. By detecting the direction of Earth's gravity vector, a linear “3D” accelerometer can be used to measure the translation (linear movement without angular rotation) of an object, and also which can sense “tilt” (such as angular accelerations associated with “roll” or “pitch”), freefall, and shock. Accelerometers of differing types and sensitivities may function by exploiting any of a variety of physical phenomena, such as the rolling of a small ball, the shifting/flowing of a conductive or heavy liquid, the swinging of a pendulum, or other mechanical means of varying accuracy and sensitivity. More sophisticated known linear accelerometers may sense movement through the Earth's magnetic field, or exploit other magnetic or optical phenomena.
However, it presently is difficult or impossible to differentiate, using conventional, cost-effective linear accelerometers, between linear motion (acceleration relative to an ordinary Cartesian coordinate system) and the change in orientation of a device and a corresponding change (i.e. angular acceleration) in roll or pitch. A change in the “heading” or yaw of a moving object cannot be sensed by conventional linear accelerometers at all. Gyroscopes, which are comparatively expensive, complex and delicate, commonly serve as the means for sensing a shift or change in rotational freedom, such as the yaw, roll and pitch, of a moveable object. Normally, three gyroscopes are used, one per axis of rotation, albeit, the latest developments in micro-electromechanical systems (MEMS) technologies allowed the development of a two-axis gyroscope. There is therefore a need in the art for a method and means for reliably measuring movement of an object in all six degrees of freedom, including changes in yaw as well as roll and pitch, using relatively simple accelerometer sensors.